如何在 Linux 上正确设置串行通信 [英] How to properly set up serial communication on Linux
问题描述
我正在尝试在 FPGA 板上读写数据.该板本身带有一个驱动程序，该驱动程序在插入该板时创建一个名为 ttyUSB0 的终端设备.在 FPGA 上，实现了异步接收器和发送器，它们似乎可以工作.
I'm attempting to read and write data from and to an FPGA board. The board itself came with a driver that create a terminal device called ttyUSB0 whenever the board is plugged in. On the FPGA, an asynchronous receiver and transmitter were implemented, and they seem to work.
但是，C 方面似乎存在问题.我一直在使用一些测试向量来测试 FPGA 是否输出了正确的信息.我注意到了一些事情:
However, there seems to be an issue on C side of things. I've been using some test vectors to test if the FPGA is outputting the proper information. I've noticed a few things things:
- 设备有时无法正确打开
- 有时无法检索或设置终端属性.
- 读取有时是非阻塞的，不会检索到正确的值.
以下是我如何设置终端和文件描述符选项.大部分内容来自这里:http://slackware.osuosl.org/slackware-3.3/docs/mini/串口编程
Below is how I set up terminal and file descriptor options. Much of it was taken from here: http://slackware.osuosl.org/slackware-3.3/docs/mini/Serial-Port-Programming
任何关于程序失败原因的建议或评论都会非常有帮助.
Any advice or comments as to why the program may be failing would be greatly helpful.
#include <stdio.h> // Standard input/output definitions
#include <string.h> // String function definitions
#include <unistd.h> // UNIX standard function definitions
#include <fcntl.h> // File control definitions
#include <errno.h> // Error number definitions
#include <termios.h> // POSIX terminal control definitions
int open_port(void){
int fd; // File descriptor for the port
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY);
if (fd == -1){
fprintf(stderr, "open_port: Unable to open /dev/ttyUSB0 %s
",strerror(errno));
exit(EXIT_FAILURE);
}
return (fd);
}
int main(void){
int fd = 0; // File descriptor
struct termios options; // Terminal options
fd = open_port(); // Open tty device for RD and WR
fcntl(fd, F_SETFL); // Configure port reading
tcgetattr(fd, &options); // Get the current options for the port
cfsetispeed(&options, B230400); // Set the baud rates to 230400
cfsetospeed(&options, B230400);
options.c_cflag |= (CLOCAL | CREAD); // Enable the receiver and set local mode
options.c_cflag &= ~PARENB; // No parity bit
options.c_cflag &= ~CSTOPB; // 1 stop bit
options.c_cflag &= ~CSIZE; // Mask data size
options.c_cflag |= CS8; // Select 8 data bits
options.c_cflag &= ~CRTSCTS; // Disable hardware flow control
// Enable data to be processed as raw input
options.c_lflag &= ~(ICANON | ECHO | ISIG);
// Set the new attributes
tcsetattr(fd, TCSANOW, &options);
////////////////////////////////////
// Simple read and write code here//
////////////////////////////////////
// Close file descriptor & exit
close(fd)
return EXIT_SUCCESS
}
更新我已经根据第一个答案修改了我的代码.这就是我现在拥有的:
UPDATE I've modified my code based on the first answer. This is what I have now:
#include <errno.h> // Error number definitions
#include <stdint.h> // C99 fixed data types
#include <stdio.h> // Standard input/output definitions
#include <stdlib.h> // C standard library
#include <string.h> // String function definitions
#include <unistd.h> // UNIX standard function definitions
#include <fcntl.h> // File control definitions
#include <termios.h> // POSIX terminal control definitions
// Open usb-serial port for reading & writing
int open_port(void){
int fd; // File descriptor for the port
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY);
if (fd == -1){
fprintf(stderr, "open_port: Unable to open /dev/ttyUSB0 %s
",strerror(errno));
exit(EXIT_FAILURE);
}
return fd;
}
int main(void){
int fd = 0; // File descriptor
struct termios options; // Terminal options
int rc; // Return value
fd = open_port(); // Open tty device for RD and WR
// Get the current options for the port
if((rc = tcgetattr(fd, &options)) < 0){
fprintf(stderr, "failed to get attr: %d, %s
", fd, strerror(errno));
exit(EXIT_FAILURE);
}
// Set the baud rates to 230400
cfsetispeed(&options, B230400);
// Set the baud rates to 230400
cfsetospeed(&options, B230400);
cfmakeraw(&options);
options.c_cflag |= (CLOCAL | CREAD); // Enable the receiver and set local mode
options.c_cflag &= ~CSTOPB; // 1 stop bit
options.c_cflag &= ~CRTSCTS; // Disable hardware flow control
options.c_cc[VMIN] = 1;
options.c_cc[VTIME] = 2;
// Set the new attributes
if((rc = tcsetattr(fd, TCSANOW, &options)) < 0){
fprintf(stderr, "failed to set attr: %d, %s
", fd, strerror(errno));
exit(EXIT_FAILURE);
}
////////////////////////////////
// Simple Read/Write Code Here//
////////////////////////////////
// Close file descriptor & exit
close(fd);
return EXIT_SUCCESS;
}
澄清一下，接收器和发送器使用 8 个数据位，1 个停止位，并且没有奇偶校验位.
Just to clarify, the receiver and transmitter use 8 data bits, 1 stop bit, and no parity bit.
推荐答案
我更喜欢 SerialPOSIX 操作系统编程指南.
您应该删除 fcntl(mainfd, F_SETFL) 语句，因为它不是必需的并且执行不正确(F_GETFL 之前没有完成并且缺少第三个参数).
You should delete the fcntl(mainfd, F_SETFL) statement, since it's not required and incorrectly implemented (F_GETFL not done prior and missing third argument).
尝试使用 cfmakeraw 设置非规范模式，因为您的初始化代码不完整:
Try using cfmakeraw to setup non-canonical mode, since your initialization code is incomplete:
options->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
| INLCR | IGNCR | ICRNL | IXON);
options->c_oflag &= ~OPOST;
对于非规范模式，还需要定义
For non-canonical mode, you also need to define
options.c_cc[VMIN] = 1;
options.c_cc[VTIME] = 2;
1 和 2 只是建议值.
1 and 2 are just suggested values.
在所有系统调用之后添加返回状态测试.
Add testing of return status after all system calls.
rc = tcgetattr(mainfd, &options);
if (rc < 0) {
printf("failed to get attr: %d, %s
", mainfd, strerror(errno));
exit (-3);
}
尝试使用较慢的波特率(例如 115200 甚至 9600)进行测试.
Try testing with slower baudrates (e.g. 115200 or even 9600).
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